Nasogastric enteral access devices (for example, NG-EADs, enteral feeding tubes, nasogastric tubes, NG tubes, feeding tubes) are widely used in patients who require nutrition to be delivered directly to the stomach due to an inability to swallow foods on their own. For example, a patient who is being mechanically ventilated through an endotracheal tube (ETT) requires an NG tube because the ETT prevents the patient from swallowing without the risk of food being aspirated into the airways.
When properly positioning an NG tube in a patient, the tube tip is inserted through the nose into the esophagus and advanced into the stomach or farther into the duodenum. To confirm proper placement, a variety of methods are used according to the prior art, including chest x-rays and testing of aspirates for a pH reading between 1 and 5.5. However, errors in placement still occur either due to misinterpretation of the results (e.g. misreading of chest x-ray), unintentionally introducing substances in the NG tube that may cause false positive pH readings (flushing tube with water prior to placement), or failing to positively confirm placement in the first place. Accidental placement of the NG tube into the airway also is an ongoing concern and can lead to catastrophic consequences when fluids that are intended for the stomach are delivered directly into the lungs. This aspiration of fluids into the lungs frequently leads to pneumonia which carries risk of serious and potentially lethal complications. Accordingly, there is a need for an improved method and system for assisting in the proper placement of NG tubes.
Several apparatuses and methods for acoustically guiding, positioning, and monitoring tubes within a body are known. See, for example, U.S. Pat. Nos. 5,445,144 and 6,705,319 to Wodicka et al., the disclosure of which is incorporated herein by reference, which disclose an apparatus and method for acoustically monitoring the position of a tube (e.g., ETT) within an anatomical conduit. In various embodiments, a sound pulse is introduced into a wave guide and is recorded as it passes by one or more microphones located in the wave guide wall. As the sound pulse is propagating down the tube, reflected sound pulses arise from changes in cross-sectional area due to constrictions that may exist in the tube. The sound pulse is then emitted through the distal tip of the ETT into the airway (or wherever in the body the tip of the ETT is located) and an acoustic reflection propagates back up the ETT to the wave guide for measurement by the same microphone(s). The amplitude and the polarity of the incident and reflected sound pulse are used to estimate the characteristics of the airway and the ETT, and thereby guide the ETT placement or monitor the ETT for patency.
Another apparatus and method for examination and measurement of constrictions of passages in a cavity by means of acoustic reflectometry is described in U.S. Pat. No. 5,823,965 to Rasmussen. Rasmussen describes an acoustic reflectometer attached to a flexible closed-ended hose which is introduced into a cavity with the distal end of the hose placed past the zone of the passage to be examined. A transducer converts an activation signal from a signal generator to an excitation signal which is sent into the interior of the hose. A response signal which depends on the local deformation of the hose in the examined zone is picked up by a transducer and subjected to analysis in relation to the excitation signal. An analysis circuit and computer give an image on screen indicating the results of the examination.
Notably, Rasmussen teaches and claims a hose having only a closed distal end. Secondly, Rasmussen teaches and claims determining the internal cross-sectional shape of the hose from the excitation and response signals while the present disclosure directly uses the reflection response signal to determine the location and degree of constrictions within the hose. The internal cross-sectional shape, or the cross-sectional area vs. distance profile, of the hose requires the additional step of calculating the profile using the Ware-Aki or similar algorithm as discussed in U.S. Pat. No. 4,326,416, which is cited by Rasmussen.